The intervertebral discs that reside between each vertebra of the spine act as shock absorbers between the vertebrae. The disc itself consists of a tough outer layer called the annulus, and soft inner material, called the nucleus. The soft nucleus absorbs the majority of the shock as the body moves, keeping the spine supple and supported. As one ages, both the annulus and the nucleus lose some of their cushioning ability, and a greater portion of the pressure is borne by the outside of the disc, the annulus.
An artificial disc (also called a disc replacement, disc prosthesis or spine arthroplasty device) is a device that is implanted into the spine to imitate the functions of a normal disc (i.e., carry load and allow motion). There are many artificial disc designs classified into two general types: total disc replacement and disc nucleus replacement. As the names imply, with a total disc replacement, all or most of the disc tissue is removed and a replacement device is implanted into the space between the vertebra. With a disc nucleus replacement, only the center of the disc (the nucleus) is removed and replaced with an implant. The outer part of the disc (the annulus) is not removed. Disc nucleus replacement surgery offers certain benefits compared to total disc replacement. Since a disc nucleus replacement device is designed to replace only the nucleus of the disc, the procedure is less time consuming and possesses less risk to surrounding structures. Another benefit of disc nucleus replacement surgery is that it results in the retention of a greater amount of tissue, which gives the disc a greater regenerative capacity.
An important aspect of disc nucleus replacement surgery is to remove all of the nucleus material before installing the nucleus replacement device. In addition, care must be taken to avoid creating too large a defect in the annular wall. Incomplete or inadequate clearance of the disc nucleus, or formation of too large an annular defect, can cause the nucleus replacement to be expelled from or to extrude from the disc space.
Accordingly, there remains a need for improved devices and methods for removing nucleus tissue from an intervertebral disc, and in particular, devices and methods for removing nucleus tissue that minimize the required annular defect.